Reciprocating slat conveyors comprise a plurality of side by side conveyor slats that are driven in one direction for advancing a load and are retracted in the opposite direction. A reciprocating slat conveyor is divided into both "sets" and "groups" of conveyor slats. The slats of each "set" move together. Each "group" includes one slat from each "set." In some slat conveyors, all slats are driven in unison, in the conveying direction, and are then retracted sequentially, one set at a time. There have been attempts to drive a majority of the conveyor slat sets in the conveying direction while simultaneously retracting the remaining conveyor slat sets, to provide a conveyor that will continuously move the load on the conveyor. These conveyors are herein referred to as continuously advancing, reciprocating slat conveyors. Examples of continuously advancing, reciprocating slat conveyors, existing in the patent literature, are disclosed by the following patents: Netherlands Patent No. 67/06657, granted Nov. 13, 1968, to Cornelis Deyer; U.S. Pat. No. 3,534,875, granted Oct. 20, 1970, to Olof A. Hallstrom; U.S. Pat No. 4,144,963, granted Mar. 20, 1979, to Olof A. Hallstrom; U.S. Pat. No. 4,580,678, granted Apr. 8, 1986, to Raymond K. Foster; U.S. Pat. No. 4,793,468, granted Dec. 27, 1988, to James M. Hamilton and Phillip J. Sweet; U.S. Pat. No. 5,063,981, granted Nov. 12, 1991, to Arvo Jonkka; U.S. Pat. No. 5,340,264, granted Aug. 23, 1994, to Manfred W. Quaeck and U.S. Pat. No. 5,469,603, granted Nov. 28, 1995, to Jimmy R. Stover. These patents should be carefully considered for the purpose of putting the present invention into proper perspective relative to the prior art.
Hamilton et al. U.S. Pat. No. 4,793,468; Quaeck U.S. Pat. No. 5,340,264; and Stover U.S. Pat. No. 5,469,603 all utilize a control system that includes solenoid operated valves. Hamilton et al. U.S. Pat. No. 4,793,468 and Quaeck U.S. Pat. No. 5,340,264 use a regenerative circuit wherein common ends of the drive units are commonly plumbed so that the hydraulic fluid from all of the advancing cylinders is forced into the retracting cylinder, to cause the retraction. In these systems, each drive unit is provided with a switching valve that is connected to the working chamber of its drive unit that is opposite the working chamber that is connected to the other drive units. The switching valve switches its working chamber between pressure and return.
Stover U.S. Pat. No. 5,469,603 discloses providing each drive unit with two valves in series. One of these valves is a reversing valve. The other is a proportional valve having a tapered metering passageway and a movable tapered flow restricter that is connected to and moved by an electromagnetic operator. The reverse valve is operated by a micro switch that is tripped when the slats reach the end of their path of travel.
There is a need for a hydraulic drive and control system for a continuously advancing, reciprocating slat conveyor that utilizes pressure and return lines, piston-cylinder drive units for moving the slat sets, a proportional directional control (PDC) valve for each drive unit that switches the working chambers of the drive units between pressure and return, and a control system for the PDC valves that uses slat position feedback for adjusting the rate of fluid movement into and out from the working chambers for maintaining a desired pattern of slat movement. An object of the present invention is to provide such a hydraulic drive and control system. There is also a need for a drive module for a continuously advancing, reciprocating slat conveyor. Another object of the invention is to provide such a drive module.